1. Field of Invention
This is a control system invention which applies speed control to consumable electrode feed devices for use with electric short-circuit metal transfer arc welders.
2. Description of Prior Art
The present invention applies to weld electrode feed motor speed control. One prior art method in this field (U.S. Pat. No. 3,731,049) adjusts the weld electrode feed motor speed as a function of the ratio between the arc-on period and the total period between short-circuits. Another prior art method in this field (U.S. Pat. No. 3,627,975) adjusts the weld electrode feed motor speed as a function of the arc-on period. Both of these prior art methods require an accurate measure of the arc-on period, therefore requiring a predefined weld power source voltage waveform in order to make possible arc-on period sensing. The present invention senses only the immediate voltage drops coincident with the weld short-circuit onsets thus elminating the requirement for a predefined weld power source voltage waveform. In addition the present invention incorporates external controls for adjusting the weld electrode feed motor speed to accomodate varying welding conditions, which neither of the prior art methods provide. Finally the present invention provides both proportional and integral type controls; the integral control for reducing steady state erroes between the desired and measured time periods between weld short-circuit onsets. Neither of the two prior art methods provide integral type control.